Particulate failures for surface-micromachined MEMS

We investigate the failure modes of a comb-drive surface-micromachined microresonator that are caused by particulate contaminations. The microresonator structure is chosen as our research vehicle because it possesses all the primitive components found in many capacitive-based MEMS sensors and actuators. Process simulation is used to create the full-spectrum of defective structures caused by foreign particles. The generated defective structures are then classified based on their geometrical properties. Finite element analysis is used to understand the impact of these defects on the mechanical frequency response of the microresonator while HSPICE simulations are performed to determine the corresponding electrical misbehaviors within an acceleration measuring application. Simulation results show that particles can cause unwanted anchors, broken beams and welded comb fingers. However, the most interesting defects are broken comb fingers and lateral finger protrusions that only affect sensing capacitance. These defects lead to a very small increase or decrease in the shuttle mass. The mass change is so small that the mechanical frequency response of the resonator is virtually unchanged. However, the HSPICE simulations show that the change in output sensing voltage can be catastrophic